The present invention relates to an endoscope apparatus with an insertion part having a small outer diameter which includes an object optical system to conduct measurements or stereoscopic-vision observations.
Applications of stereoscopic-vision and measurement endoscopes include, for instance, the following fields: inspection of supply pipes of cooling water in nuclear power stations; inspection of turbine blades of steam generators in power plants; and inspection of aircraft engines. In medical applications, they may also be applied to surgery using an endoscope.
In any case, flaws and cracks of related parts, or size and depth of an affected area can be measured without disassembly or laparotomy, and its servicing or operation can be effectively conducted in safety by use of stereoscopic-vision.
Conventional stereoscopic-vision and measurement endoscopes will be described with reference to FIGS. 8 to 13. Heretofore, in order to obtain a parallax for the stereoscopic-vision and measurement, it has been widely known to align two identical right and left optical systems in parallel with each other. However, an inevitable error between the right and left optical systems does not allow the right and left images to be identical to each other. In the stereoscopic-vision, the resulting difference between the right and left images produces a fusion-image of the right and left images for an observer, which causes observer""s fatigue. This difference also causes a measurement error in a measurement. Thus, in order to lessen the fatigue and error, it is required to minimize the number of parts in the right and left optical systems. The following two prior arts references provide a means to solve this: Japanese Patent Laid-Open Publication No. Hei 8-122665 (U.S. Pat. No. 5,743,846) shown in FIG. 9; and Japanese Patent Laid-Open Publication No. Hei 11-006967 (U.S. Pat. No. 5,971,915) shown in FIG. 10.
These prior arts references each provide right and left optical systems partially having the same right and left parts, which are expected to reduce the error. However, a brightness diaphragm 55 of the prior arts comprises two apertures each of which corresponds to the respective objective lenses positioned in parallel. This involves a disparity of each aperture to the corresponding optical axis and an error between the respective right and left apertures, which leads to an error between the right and left images.
A prior art reference in which a brightness diaphragm has one unified aperture is disclosed by Japanese Patent Laid-Open Publication No. Hei 11-109257 shown in FIG. 8. In this prior art reference, a brightness diaphragm 54 having one aperture may solve the above-mentioned problem. However, focusing a real image on the end surface 9 of each objective lens runs into following three problems.
First, a combined dimension of objective lenses 121, 122 and relay lenses 50, 54, 6 in the direction of an optical axis is lengthened, because the real images are formed by the objective lenses 121, 122 which have a positive focal distance and are positioned in parallel at a top of the endoscope, and the dimension of these objective lenses directly makes the overall length of the endoscope longer. Further, a rigid section (i.e. unbendable section) will be undesirably lengthened.
Second, if some contamination intrudes and is attached on the end surface 9 of the objective lens in the manufacturing process, the contamination overlapped with the real image is reflected into the image, which undesirably disturbs the stereoscopic-vision and measurement.
Third, since the real image is focused into a final image on an image pickup device by relaying the real image, the real image 9 directed to an axial direction of the endoscope is inverted and formed as the image directed outward at the image pickup device 7. Thus, the right-and-left state of a displayed image on a monitor will be in a state of counterchanging the right and left which are generally recognized by humans. Specifically, an image to be fundamentally monitored by a right eye will be an image for a left eye. Consequently, this prior art undesirably provides a reverse-stereoscopic-vision in which information in the direction of stereopsis is reversed for the right and left.
Further, the prior art is a top afocal adapter type of endoscope. FIG. 11 shows a general view of the top afocal adapter type of endoscope. FIG. 13 is a sectional view showing an objective optical system in the top section of the endoscope. As shown in FIGS. 11 to 13, a top afocal adapter 5 is detachable from an endoscope body 4. Referring to FIG. 13, a master lens 6 is provided in the endoscope body 4, and adjusts to make a focal point locate approximately at infinity to an image pickup device 7. A top afocal adapter 5 may have different field angles and line of sights suitable for observation purposes, and also may be detachably at a position X on the object side of the master lens. FIG. 13(a) shows the state when the top afocal adapter 5 is attached to the endoscope body 4. FIG. 13(b) shows the state when it is detached. The top afocal adapter 5 is designed and produced to bring emergent rays of respective field angles substantially into parallel rays to an optical axis (i.e. afocal) at the position X, so as to form an image on the image pickup device, when the top afocal adapter is attached. The top afocal adapter type of endoscope is economically advantageous because the expensive endoscope body may be used in common with it. In addition, since the detached section is afocal, the diameter of luminous flux is thick and no real image is formed in the detached section. Thus, the affect of contaminations is practically inconspicuous, and the focal shift caused by misregistration in the attaching operation has an insignificant impact.
In summary, the above discussed prior art systems have an error between the right and left images due to the brightness diaphragm 55 having two apertures. Further, the prior art systems do not describe an end afocal endoscope nor a structure for an adapter type of endoscope. The prior art has the problems of a lengthened rigid section, a disturbed observation by contaminations and an occurrence of reverse-stereoscopic-vision.
It is an object of the present invention to provide stereoscopic-vision and measurement endoscopes capable of having a short rigid section without any disturbance of contaminations to an observation and any occurrence of reverse-stereoscopic-vision as well as its capability of applying an end afocal adapter.
In order to achieve the aforementioned object, according to one aspect of the present invention, there is provided an endoscope having an insertion part which includes an object optical system to conduct measurements or stereoscopic-vision observations, the object optical system comprising, in turn from an object side to an image side, a first unit, a second unit, a brightness diaphragm, a third unit, and an image pickup unit. The first unit includes an object cover glass, a pair of negative lenses arranged in parallel and almost in contact with each other, and a pair of field masks corresponding to the pair of negative lenses, respectively, wherein a principal ray emergent to the image side in each of the pair of negative lenses is parallel to each optical axis of the pair of negative lenses. The second unit includes a flare mask having an analogous form which corresponds to the range of the field mask, and a first positive lens having an optical axis which is positioned eccentrically to at least one of the optical axes of the pair of negative lenses, wherein the first positive lens forms no real image within the second and third units. The brightness diaphragm includes a single aperture section and an adapter cover glass, the brightness diagram being positioned at a back-focus-position of the first positive lens of the second unit, wherein each optical axis of the pair of negative lenses passes through the single aperture section, the single aperture section being positioned unitarily with the adapter cover glass. The third unit includes a master cover glass, and a second positive lens capable of focusing on an infinity-distance-object, wherein the following equation (1) is satisfied as a condition to enable the second positive lens to focus on the infinity-distance-object:
|xcfx86a/xcfx86| less than 0.1xe2x80x83xe2x80x83(1) 
where xcfx86a is a combined power of the first unit and the second unit, and xcfx86 is an combined power of the first to third units. The image pickup unit includes an infrared cut off filter, and an image pickup device positioned at a back-focus-position of the second positive lens of the third unit, the image pickup device being single and having 2 to 2.5 mm or less of effective image pickup range. Further, the first unit, the second unit, and the brightness diaphragm are comprised in an adapter so as to be detachable from the third unit and the image pickup unit at a boundary between the adapter cover glass and the master cover glass.
According to a second aspect of the present invention, there is also provided an endoscope apparatus including an object optical system to conduct measurements or stereoscopic-vision observations, the object optical system comprising, in turns from an object side to an image side, a first unit, a second unit, a third unit, and an image pickup unit. The first unit includes negative lenses. The second unit includes a first positive lens, wherein the first positive lens forms no real image in the range of the second unit to the third unit. The third unit includes a second positive lens. The image pickup unit includes a single image pick up device.
In the second aspect of the present invention, the second positive lens of the third unit may be capable of approximately focusing on an infinity-distance-object, wherein the following equation (1) is satisfied as a condition to approximately enable the second positive lens to focus on the infinity-distance-object:
|xcfx86a/xcfx86| less than 0.1xe2x80x83xe2x80x83(1) 
where xcfx86a is a combined power of the first unit and the second unit, and xcfx86 is an overall combined power of the first to third units. The endoscope apparatus may further include a brightness diaphragm having a single aperture section, and the brightness diaphragm may be positioned approximately at a back-focus-position of the first positive lens of the second unit.
Further, the negative lenses of the first unit may be a pair of negative lenses arranged in parallel and almost in contact with each other, and the first positive lens may have an optical axis positioned eccentrically to at least one of the optical axes of the pair of negative lenses.
In this case, the pair of negative lenses may include a lens having a concave surface which is directed to the object side. Further, the pair of negative lenses may include a pair of first concave lenses and a pair of second concave lenses, wherein the pair of first concave lenses is either a single lens or cemented lens, which has a concave surface as a final surface on the image side, the concave surface being directed to the image side, and the pair of second concave lenses is either a single lens or cemented lens, which has a convex surface as a final surface on the image side, the convex surface being directed to the image side.
The pair of negative lenses may have a cutout portion at their circumferences, wherein each of said negative lenses abuts with each other at the cutout portion such that the distance between the centers of the circumferences is less than the sum of the radii thereof.
In the second aspect of the present invention, the endoscope apparatus may further include a brightness diaphragm having two aperture sections, the brightness diaphragm being positioned either at the object side or at the image side within the second unit. The negative lenses of the first unit may include a pair of negative lenses arranged in parallel and almost in contact with each other, and the first positive lens has an optical axis which is positioned eccentrically to at least one of the optical axes of the pair of negative lenses. The first positive lens may include a first lens and second lens, wherein the first lens is a positive power lens and has a convex surface directed to and located proximately to the object side, and the second lens is a negative power lens and has a concave surface directed to and located proximately to the object side.
In the second aspect of the present invention, the endoscope apparatus may further include an object cover glass provided on the object side in the first unit, a prism provided on the object side in the first unit to convert a line of sight, a field mask provided in the first unit, the field mask corresponding to the negative lenses, a flare mask provided in the second unit, or a master cover glass provided proximally to the object side in the third unit.
Further, the first unit and the second unit may be comprised in an adapter so as to be detachable to the third unit and the image pickup unit. In this case, the endoscope apparatus may further include a brightness diaphragm and an adapter cover glass unitarily positioned with the brightness diaphragm. The image pickup device may be positioned at a back-focus-position of the second positive lens of the third unit, and the image pickup device is singe and has 2 to 2.5 mm or less of effective image pickup range.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description.